This invention relates to electrical image processing systems. Specifically, this invention relates to method and apparatus for touching up an electrical, continuous tone image upon operator interaction with a visual representation of the image on a display screen.
The publishing industry, for one, employs high resolution optical scanners to generate electrical, continuous tone raster image signals representative of continuous tone originals such as photographs and graphic art work. The raster image signals are used in electronic plate making equipment to modulate a scanning laser beam, an electron beam in a cathode ray tube (CRT) or the like to construct a facsimile of the continuous tone original on a suitable printing master. The content of an original must be in final form before the scanner generates the raster signals. The reason is that presently known electronic plate making systems have limited provisions for making changes to the electrical image like touch up by a graphic artist.
A touch up artist typically: changes shading; changes tone levels; corrects color hue; erases small, randomly located defects; fills in erased regions; adds a script signature; adds detail by free hand; and makes notations on the original. The changes or touch ups made by the artist usually result in an original being refabricated before it is suitable to be optically scanned. This, of course, is costly and increases editorial difficulties when the time needed to make a change is not available. The editing or correction operation is particularly complex when the original includes three or four color separation images which all need to be corrected.
A tool called an "airbrush" is used in the graphic arts to do at least some touch up work. The airbrush is a spray gun about the size of a pencil with a nozzle at the tip. The gun is coupled to a positive air source to spray watercolor pigments and is used to correct or obtain a given tone or to graduate the tone between two regions of different tone. In the plate-making process, the airbrush is used to direct a stream of an abrasive-like pumice onto a plate to remove spots or other unwanted areas. The electrical airbrush of the present invention is significantly different from that used in the graphic arts but the name is borrowed because it tends to be a helpful functional descriptor. One significant feature of the electrical airbrush totally lacking with a pneumatic airbrush is that tone or image density can be increased as well as decreased.